1. Field of the Invention
The present invention relates to a synthetic resin composition having good lubricating properties when immersed in a liquid particularly water and a method of manufacturing a bearing having a low coefficient of friction underwater.
2. Description of Related Art
Conventionally, bearings for pumps which are used in a liquid such as a water are shielded to prevent the liquid from entering into the bearings. Shieldless bearings have also been used. However, prior art materials for shieldless bearings have not exhibited desired low friction characteristics when immersed in water or other liquids.
As much as 900,000 tons/year and 33,000,000 tons/year of rice bran is produced and wasted in Japan and in the world, respectively. Attempts have been made to find uses for this material. Rice bran has employed to produce a porous carbon composition. (cf. xe2x80x9cKinou Zairyou (Function and Materials)xe2x80x9d, Vol. 17, No. 5, pp. 24-28, May 1997); and U.S. Pat. No. 5,916,499.
The Function and Materials article teaches a RB ceramic composition (hereinafter referred to as RBC) and its production method. A RBC is a carbon composition. Defatted rice bran and a thermosetting resin were mixed and kneaded together, and then molded under pressure. The molded composition is dried. The dried molded composition is sintered under an inert atmosphere to produce the carbon composition. Here, any thermosetting resin can be used in the process as long as it has thermosetting properties. Typical examples of such thermosetting resins include phenol resins, diarylphthalate resins, unsaturated polyester resins, epoxy resins, polyimide resins and triazine resins. Phenol resins are preferably used. A mixing ratio between defatted rice bran and a thermosetting resin is 50:50 to 90:10 by weight, preferably 75:25.
A sintering temperature is 700xc2x0 C.xcx9c1,000xc2x0 C., and a rotary kiln is usually employed. The sintering duration is approximately 40 to 120 minutes.
The RB ceramic composition-can be further improved to furnish a carbon composition called a CRB ceramic composition (hereinafter referred to as CRBC). Defatted rice bran is prepared from rice bran. Defatted rice bran and a thermosetting resin produce a RB ceramic composition as described above. The sintered RBC composition is crushed into carbonized powder with particle sizes of no larger than approximately 100 mesh. The carbonized powder and a thermosetting resin are mixed, kneaded and molded under pressure of 20 MPaxcx9c30 MPa. Then, the molded composition is again thermally treated at 500xc2x0 C.xcx9c1,100xc2x0 C. under an inert atmosphere to produce a black resin or porous ceramic composition, which is CRBC.
According to the invention, a synthetic resin composition for making bearings having a desirable a low coefficient of friction when submersed in a liquid is provided. In addition, a method of making a low friction bearing for use under liquid is provided as well as a low friction bearing for use under liquid.
According to the invention, a synthetic resin composition with lubricative underwater properties is provided. The resin is useful for making articles that desirably exhibit a low coefficient of friction under liquid particularly underwater. A powder preferably a fine powder of a RBC, CRBC or both are uniformly dispersed in a synthetic resin. Desirably the weight ratio between RBC or CRBC powders and the synthetic resin is 30:90 to 70:10.
In another aspect of the invention, a method of making a bearing having a low coefficient of friction and having lubricity when immersed in liquid is provided. A rice bran ceramic (RBC) fine powder is formed by mixing defatted rise bran with a thermosetting resin. The rice bran and the thermosetting resin are molded under pressure to form a first molded composition. The molded composition is then dried and sintered and crushed into a fine powder. A bearing is then formed by mixing the RBC fine powder with a synthetic resin preferably a thermoplastic resin under sufficient heat to form a homogeneous mixture having plasticity.
Alternatively RBC is used to form a carbon rice brand ceramic (CRBC) fine powder. RBC powder is mixed with a thermosetting resin, molded, sintered and crushed to a fine powder CRBC. The CRBC fine powder or both the CRBC fine powder and the RBC fine powder are mixed with a synthetic resin preferably a thermoplastic resin under sufficient heat to form a homogeneous mixture having plasticity. A bearing is then fabricated for example by molding the homogeneous mixture. As a result a bearing is provided having a low coefficient of friction when submersed under a liquid preferably underwater.
The preferred embodiment of the present invention is illustrated in the drawings and examples. However, it should be expressly, understood that the present invention should not be limited solely to the illustrative embodiment.
RBC and CRBC have excellent characteristics for use as a material for use in fabricating bearings. RBC and CRBC exhibit high hardness, irregular particle shapes when they are made into powder, a very small expansion coefficient, porous composition structure and electrically conductive. They are light weight, have a low specific weight and exhibit a very low friction coefficient and excellent abrasion resistance. Moreover, use of RBC and CRBC has little adverse effects on the global environment and contributes to the conservation of resources because they are made from rice bran.
According to the invention, a synthetic resin composition having lubricative under liquid properties is provided for use as a material for fabricating bearings which have a low coefficient of friction when immersed in a liquid particularly underwater. Desirably the bearings made according to the invention have a low coefficient of friction in water, alcohol, ethylene glycol, and mixtures thereof preferably in water. In another aspect of the invention, a method of making a low friction bearing having good sliding properties under liquid preferably underwater is provided as well as a low friction bearing having a low coefficient of friction under liquid preferably for use underwater.
According to the invention, a synthetic resin composition with lubricative under liquid preferably lubricative underwater properties is provided. A powder, preferably a fine powder of a RBC, CRBC or both are uniformly dispersed in a synthetic resin preferably a thermoplastic resin. Desirably the weight ratio between the powder of RBC or CRBC and the synthetic resin is 30:90 to 70:10. A variety of synthetic resins can be employed in the present invention. Preferably the resin is a thermoplastic resins desirably polyamide, polyester or polyolefin resins.
Desirable thermoplastic resins for use in the invention such as nylon-66 (polyhexamethyleneadipamide), nylon-6(polycapramide), nylon-11(polyundecaneamide), nylon-12, polyacetal, polybutyleneterephthalate, polyethyleneterephthalate, polypropylene, polyethylene, and/or polyphenylenesulfide, preferably Nylon-66. A single thermoplastic resin can be used, optionally two or more thermoplastic resins can be mixed and employed.
According to the invention, a thermosetting resin also can be included in the composition in an amount up to approximately 20% by weight of the entire composition. Thermosetting resins include for example phenol resins, diarylphthalate resins, unsaturated polyester resins, epoxy resins, polyimide resins and triazine resins.
In another aspect of the invention, a method of making a bearing having a low coefficient of friction under liquid preferably underwater and having lubricity when immersed in liquid is provided. A rice bran ceramic (RBC) fine powder is formed by mixing defatted rise bran with a thermosetting resin. The rice bran and the thermosetting setting resin are molded under pressure to form a molded composition. The molded composition is then dried and sintered and crushed into a fine powder. The RBC fine powder is mixed with a synthetic resin preferably a thermoplastic resin under sufficient heat to form a homogeneous mixture having plasticity. A bearing is then fabricated for example by molding the homogeneous mixture. As a result a bearing is provided having a low coefficient of friction when submersed under a liquid preferably under water.
Alternatively RBC is used to form a carbon rice brand ceramic (CRBC) fine powder. RBC powder is mixed with a thermosetting resin molded, sintered and crushed to a fine powder CRBC. The CRBC fine powder or both the CRBC fine powder and the RBC fine powder are mixed with a synthetic resin preferably a thermoplastic resin under sufficient heat to form a homogeneous mixture having plasticity. A bearing is then fabricated for example by molding from the homogeneous mixture. As a result a bearing is provided having a low coefficient of friction and exhibiting lubricity when submersed under a liquid preferably underwater.
According to the invention, the average particle diameter of fine powder of RBC or CRBC is desirably 300 xcexcm or less. Preferably, an average particle diameter of 10 to 100 xcexcm is used and more preferably an average particle diameter of 10 to 50 xcexcm is used.
The bearings according to the invention are molded from the synthetic resin composition prepared as described above. Molding is preferably performed using extrusion or injection molding; It is desired that relatively low mold temperature be employed. Generally, a temperature in the vicinity of a glass transition point or melting point of the synthetic resin is desirable. Moreover, gradual cooling of the mold is desired to obtain molded pieces with better friction characteristics than rapid cooling.
The synthetic resin composition according to the invention has a variety of uses. For example, it can be used as a general bearing material including for bearings used in an underwater pump. Such use takes advantage of its low friction and abrasion characteristics. In addition, due to its excellent electrical conductivity, the resin composition can be used for applications such as a key cap. Because of its excellent dispersion characteristics, various other types of molded pieces can be made with the synthetic resin composition containing fine powder of a RBC or CRBC as well.